//
//
// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//

#ifndef GRPC_SRC_CORE_LIB_CHANNEL_CHANNEL_STACK_H
#define GRPC_SRC_CORE_LIB_CHANNEL_CHANNEL_STACK_H

//////////////////////////////////////////////////////////////////////////////
// IMPORTANT NOTE:
//
// When you update this API, please make the corresponding changes to
// the C++ API in src/cpp/common/channel_filter.{h,cc}
//////////////////////////////////////////////////////////////////////////////

// A channel filter defines how operations on a channel are implemented.
// Channel filters are chained together to create full channels, and if those
// chains are linear, then channel stacks provide a mechanism to minimize
// allocations for that chain.
// Call stacks are created by channel stacks and represent the per-call data
// for that stack.

// Implementations should take care of the following details for a batch -
// 1. Synchronization is achieved with a CallCombiner. View
// src/core/lib/iomgr/call_combiner.h for more details.
// 2. If the filter wants to inject an error on the way down, it needs to call
// grpc_transport_stream_op_batch_finish_with_failure from within the call
// combiner. This will cause any batch callbacks to be called with that error.
// 3. If the filter wants to inject an error on the way up (from a callback), it
// should also inject that error in the recv_trailing_metadata callback so that
// it can have an effect on the call status.
//

#include <stddef.h>

#include <functional>
#include <memory>

#include <grpc/event_engine/event_engine.h>
#include <grpc/grpc.h>
#include <grpc/slice.h>
#include <grpc/status.h>
#include <grpc/support/log.h>
#include <grpc/support/port_platform.h>
#include <grpc/support/time.h>

#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/channel/channel_fwd.h"
#include "src/core/lib/debug/trace.h"
#include "src/core/lib/gprpp/manual_constructor.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/gprpp/time.h"
#include "src/core/lib/gprpp/unique_type_name.h"
#include "src/core/lib/iomgr/call_combiner.h"
#include "src/core/lib/iomgr/closure.h"
#include "src/core/lib/iomgr/error.h"
#include "src/core/lib/iomgr/polling_entity.h"
#include "src/core/lib/promise/arena_promise.h"
#include "src/core/lib/resource_quota/arena.h"
#include "src/core/lib/transport/call_final_info.h"
#include "src/core/lib/transport/transport.h"
#include "src/core/telemetry/metrics.h"
#include "src/core/util/time_precise.h"

struct grpc_channel_element_args {
  grpc_channel_stack* channel_stack;
  grpc_core::ChannelArgs channel_args;
  int is_first;
  int is_last;
};
struct grpc_call_element_args {
  grpc_call_stack* call_stack;
  const void* server_transport_data;
  const grpc_slice& path;
  gpr_cycle_counter start_time;  // Note: not populated in subchannel stack.
  grpc_core::Timestamp deadline;
  grpc_core::Arena* arena;
  grpc_core::CallCombiner* call_combiner;
};

// Channel filters specify:
// 1. the amount of memory needed in the channel & call (via the sizeof_XXX
//    members)
// 2. functions to initialize and destroy channel & call data
//    (init_XXX, destroy_XXX)
// 3. functions to implement call operations and channel operations (call_op,
//    channel_op)
// 4. a name, which is useful when debugging

// Members are laid out in approximate frequency of use order.
struct grpc_channel_filter {
  // Called to eg. send/receive data on a call.
  // See grpc_call_next_op on how to call the next element in the stack
  void (*start_transport_stream_op_batch)(grpc_call_element* elem,
                                          grpc_transport_stream_op_batch* op);
  // Called to handle channel level operations - e.g. new calls, or transport
  // closure.
  // See grpc_channel_next_op on how to call the next element in the stack
  void (*start_transport_op)(grpc_channel_element* elem, grpc_transport_op* op);

  // sizeof(per call data)
  size_t sizeof_call_data;
  // Initialize per call data.
  // elem is initialized at the start of the call, and elem->call_data is what
  // needs initializing.
  // The filter does not need to do any chaining.
  // server_transport_data is an opaque pointer. If it is NULL, this call is
  // on a client; if it is non-NULL, then it points to memory owned by the
  // transport and is on the server. Most filters want to ignore this
  // argument.
  // Implementations may assume that elem->call_data is all zeros.
  grpc_error_handle (*init_call_elem)(grpc_call_element* elem,
                                      const grpc_call_element_args* args);
  void (*set_pollset_or_pollset_set)(grpc_call_element* elem,
                                     grpc_polling_entity* pollent);
  // Destroy per call data.
  // The filter does not need to do any chaining.
  // The bottom filter of a stack will be passed a non-NULL pointer to
  // \a then_schedule_closure that should be passed to GRPC_CLOSURE_SCHED when
  // destruction is complete. \a final_info contains data about the completed
  // call, mainly for reporting purposes.
  void (*destroy_call_elem)(grpc_call_element* elem,
                            const grpc_call_final_info* final_info,
                            grpc_closure* then_schedule_closure);

  // sizeof(per channel data)
  size_t sizeof_channel_data;
  // Initialize per-channel data.
  // elem is initialized at the creating of the channel, and elem->channel_data
  // is what needs initializing.
  // is_first, is_last designate this elements position in the stack, and are
  // useful for asserting correct configuration by upper layer code.
  // The filter does not need to do any chaining.
  // Implementations may assume that elem->channel_data is all zeros.
  grpc_error_handle (*init_channel_elem)(grpc_channel_element* elem,
                                         grpc_channel_element_args* args);
  // Post init per-channel data.
  // Called after all channel elements have been successfully created.
  void (*post_init_channel_elem)(grpc_channel_stack* stk,
                                 grpc_channel_element* elem);
  // Destroy per channel data.
  // The filter does not need to do any chaining
  void (*destroy_channel_elem)(grpc_channel_element* elem);

  // Implement grpc_channel_get_info()
  void (*get_channel_info)(grpc_channel_element* elem,
                           const grpc_channel_info* channel_info);

  // The name of this filter
  grpc_core::UniqueTypeName name;
};
// A channel_element tracks its filter and the filter requested memory within
// a channel allocation
struct grpc_channel_element {
  const grpc_channel_filter* filter;
  void* channel_data;
};

// A call_element tracks its filter, the filter requested memory within
// a channel allocation, and the filter requested memory within a call
// allocation
struct grpc_call_element {
  const grpc_channel_filter* filter;
  void* channel_data;
  void* call_data;
};

// A channel stack tracks a set of related filters for one channel, and
// guarantees they live within a single malloc() allocation
struct grpc_channel_stack {
  grpc_stream_refcount refcount;
  size_t count;
  // Memory required for a call stack (computed at channel stack
  // initialization)
  size_t call_stack_size;
  // TODO(ctiller): remove this mechanism... it's a hack to allow
  // Channel to be separated from grpc_channel_stack's allocation. As the
  // promise conversion continues, we'll reconsider what grpc_channel_stack
  // should look like and this can go.
  grpc_core::ManualConstructor<std::function<void()>> on_destroy;

  grpc_core::ManualConstructor<
      std::shared_ptr<grpc_event_engine::experimental::EventEngine>>
      event_engine;

  grpc_event_engine::experimental::EventEngine* EventEngine() const {
    return event_engine->get();
  }

  grpc_core::ManualConstructor<
      grpc_core::GlobalStatsPluginRegistry::StatsPluginGroup>
      stats_plugin_group;

  // Minimal infrastructure to act like a RefCounted thing without converting
  // everything.
  // It's likely that we'll want to replace grpc_channel_stack with something
  // less regimented once the promise conversion completes, so avoiding doing a
  // full C++-ification for now.
  void IncrementRefCount();
  void Unref();
  void Unref(const grpc_core::DebugLocation& location, const char* reason);
  grpc_core::RefCountedPtr<grpc_channel_stack> Ref() {
    IncrementRefCount();
    return grpc_core::RefCountedPtr<grpc_channel_stack>(this);
  }
};

// A call stack tracks a set of related filters for one call, and guarantees
// they live within a single malloc() allocation
struct grpc_call_stack {
  // shared refcount for this channel stack.
  // MUST be the first element: the underlying code calls destroy
  // with the address of the refcount, but higher layers prefer to think
  // about the address of the call stack itself.
  grpc_stream_refcount refcount;
  size_t count;

  // Minimal infrastructure to act like a RefCounted thing without converting
  // everything.
  // grpc_call_stack will be eliminated once the promise conversion completes.
  void IncrementRefCount();
  void Unref();
  grpc_core::RefCountedPtr<grpc_call_stack> Ref() {
    IncrementRefCount();
    return grpc_core::RefCountedPtr<grpc_call_stack>(this);
  }
};

// Get a channel element given a channel stack and its index
grpc_channel_element* grpc_channel_stack_element(grpc_channel_stack* stack,
                                                 size_t i);
// Get the last channel element in a channel stack
grpc_channel_element* grpc_channel_stack_last_element(
    grpc_channel_stack* stack);

// A utility function for a filter to determine how many other instances
// of the same filter exist above it in the same stack.  Intended to be
// used in the filter's init_channel_elem() method.
size_t grpc_channel_stack_filter_instance_number(
    grpc_channel_stack* channel_stack, grpc_channel_element* elem);

// Get a call stack element given a call stack and an index
grpc_call_element* grpc_call_stack_element(grpc_call_stack* stack, size_t i);

// Determine memory required for a channel stack containing a set of filters
size_t grpc_channel_stack_size(const grpc_channel_filter** filters,
                               size_t filter_count);
// Initialize a channel stack given some filters
grpc_error_handle grpc_channel_stack_init(
    int initial_refs, grpc_iomgr_cb_func destroy, void* destroy_arg,
    const grpc_channel_filter** filters, size_t filter_count,
    const grpc_core::ChannelArgs& args, const char* name,
    grpc_channel_stack* stack);
// Destroy a channel stack
void grpc_channel_stack_destroy(grpc_channel_stack* stack);

// Initialize a call stack given a channel stack. transport_server_data is
// expected to be NULL on a client, or an opaque transport owned pointer on the
// server.
grpc_error_handle grpc_call_stack_init(grpc_channel_stack* channel_stack,
                                       int initial_refs,
                                       grpc_iomgr_cb_func destroy,
                                       void* destroy_arg,
                                       const grpc_call_element_args* elem_args);
// Set a pollset or a pollset_set for a call stack: must occur before the first
// op is started
void grpc_call_stack_set_pollset_or_pollset_set(grpc_call_stack* call_stack,
                                                grpc_polling_entity* pollent);

#ifndef NDEBUG
#define GRPC_CALL_STACK_REF(call_stack, reason) \
  grpc_stream_ref(&(call_stack)->refcount, reason)
#define GRPC_CALL_STACK_UNREF(call_stack, reason) \
  grpc_stream_unref(&(call_stack)->refcount, reason)
#define GRPC_CHANNEL_STACK_REF(channel_stack, reason) \
  grpc_stream_ref(&(channel_stack)->refcount, reason)
#define GRPC_CHANNEL_STACK_UNREF(channel_stack, reason) \
  grpc_stream_unref(&(channel_stack)->refcount, reason)
#else
#define GRPC_CALL_STACK_REF(call_stack, reason) \
  do {                                          \
    grpc_stream_ref(&(call_stack)->refcount);   \
    (void)(reason);                             \
  } while (0);
#define GRPC_CALL_STACK_UNREF(call_stack, reason) \
  do {                                            \
    grpc_stream_unref(&(call_stack)->refcount);   \
    (void)(reason);                               \
  } while (0);
#define GRPC_CHANNEL_STACK_REF(channel_stack, reason) \
  do {                                                \
    grpc_stream_ref(&(channel_stack)->refcount);      \
    (void)(reason);                                   \
  } while (0);
#define GRPC_CHANNEL_STACK_UNREF(channel_stack, reason) \
  do {                                                  \
    grpc_stream_unref(&(channel_stack)->refcount);      \
    (void)(reason);                                     \
  } while (0);
#endif

inline void grpc_channel_stack::IncrementRefCount() {
  GRPC_CHANNEL_STACK_REF(this, "smart_pointer");
}

inline void grpc_channel_stack::Unref() {
  GRPC_CHANNEL_STACK_UNREF(this, "smart_pointer");
}

inline void grpc_channel_stack::Unref(const grpc_core::DebugLocation&,
                                      const char* reason) {
  GRPC_CHANNEL_STACK_UNREF(this, reason);
}

inline void grpc_call_stack::IncrementRefCount() {
  GRPC_CALL_STACK_REF(this, "smart_pointer");
}

inline void grpc_call_stack::Unref() {
  GRPC_CALL_STACK_UNREF(this, "smart_pointer");
}

// Destroy a call stack
void grpc_call_stack_destroy(grpc_call_stack* stack,
                             const grpc_call_final_info* final_info,
                             grpc_closure* then_schedule_closure);

// Ignore set pollset{_set} - used by filters if they don't care about pollsets
// at all. Does nothing.
void grpc_call_stack_ignore_set_pollset_or_pollset_set(
    grpc_call_element* elem, grpc_polling_entity* pollent);
// Call the next operation in a call stack
void grpc_call_next_op(grpc_call_element* elem,
                       grpc_transport_stream_op_batch* op);
// Call the next operation (depending on call directionality) in a channel
// stack
void grpc_channel_next_op(grpc_channel_element* elem, grpc_transport_op* op);
// Pass through a request to get_channel_info() to the next child element
void grpc_channel_next_get_info(grpc_channel_element* elem,
                                const grpc_channel_info* channel_info);

// Given the top element of a channel stack, get the channel stack itself
grpc_channel_stack* grpc_channel_stack_from_top_element(
    grpc_channel_element* elem);
// Given the top element of a call stack, get the call stack itself
grpc_call_stack* grpc_call_stack_from_top_element(grpc_call_element* elem);

void grpc_channel_stack_no_post_init(grpc_channel_stack* stk,
                                     grpc_channel_element* elem);

#endif  // GRPC_SRC_CORE_LIB_CHANNEL_CHANNEL_STACK_H
